Spectral Characterization of Silver Nanoparticles Biosynthesized from Lysinibacillus fusiformis and its Antibacterial Efficacy Against Multidrug-Resistant Bacteria Isolated from Chronic Wounds

Morbidity and mortality associated with multidrug-resistant (MDR) bacterial infections remain very high. There is a need to assess the in vitro antibacterial efficacy of novel therapeutic agents against MDR bacteria. Silver nanoparticles (AgNPs) were intracellularly synthesized by inoculating 2 g biomass of Lysinibacillus fusiformis into 300 mL of 1 mM AgNO₃ solution and incubated at 30 °C for 72 h. The AgNPs colloidal suspension was monitored via color change and UV–vis spectroscopy and subsequently characterized via scanning electron microscope (SEM), dynamic light scattering (DLS), transmission electron microscope (TEM), energy dispersive x-ray (EDX), Fourier transform infrared (FTIR), and x-ray diffractometer (XRD), analyses. Antibacterial activities of AgNPs against the MDR bacteria isolated from chronic wounds were assessed using the well-diffusion method, and the minimum inhibitory and bactericidal concentrations were determined. The biomass of Lysinibacillus fusiformis produced AgNPs colloidal suspension with dark brown color and UV–vis absorption peaks between 381 and 404 nm. The AgNPs are spherical and isolated, with a size distribution of 98.88 ± 1.46 nm and a polydispersity index of 0.231 ± 0.003. However, TEM revealed the AgNPs had an average diameter of 18.42 ± 1.47 nm and 73.89% of zerovalent silver with a strong signal at 3.0 keV. FTIR showed the presence of primary amines, while sharp Bragg’s peaks matching with the planes (111, 200, 220, and 311) of face-centered, cubic, and crystalline silver were detected for XRD. The AgNPs showed effective antibacterial efficacy against the tested MDR bacterial pathogens with P. aeruginosa (11) and Enterobacter hormaechei (19) being the most sensitive (MIC 156.25 µg/mL; MBC 312.5 – 625 µg/mL). This suggests that in vivo studies should be conducted to further establish their efficacy and possible translation to human clinical use.